The invention relates to a device having a tool holder, which can be displaced in an x direction and a z direction which is perpendicular to the x direction, and a tool in the form of a metering head, which is secured to the tool holder. A further aspect of the invention relates to weighing out a desired quantity of substance using a device of this type.
Devices of this type are used, inter alia, for automatically metering substances into a plurality of reaction vessels or test tubes which are arranged, for example, next to one another.
In a device which is known as Caco-2 Assay produced by Mettler Toledo Bohdan, Greifensee, Switzerland, there are two tool holders with different tools. The tool holders can be displaced in a horizontal x direction, a horizontal y direction which is perpendicular to the x direction, and a vertical z direction which is perpendicular to the x and y directions, and in this way can serve reaction vessels arranged next to one another under the control of software. One of the tools is designed for metering liquid as a metering head in the form of a four-needle head with four parallel hollow needles which can be spread apart. The other tool is a gripper for handling substance plates which have a multiplicity of recesses for holding substance. To weigh matter which can be handled by the device, there is a balance, on which, by way of example, a corresponding substance plate or a test tube is placed.
Although the two fixedly installed tools do make it possible to handle liquids and solids, they do not, for example, allow a solid to be metered directly into a reaction vessel. Moreover, there are two tool holders which have to be able to move independently of one another, in which context it must be ensured that they do not collide with one another. Finally, accurate weighing out of a defined quantity of substance is relatively complex.
DE 40 02 255 A1 has disclosed a fixedly mounted device for metering liquids by dispensing them from at least one metering valve connected to a liquid reservoir, which device has a main balance on which a vessel for holding liquid can be positioned. This main balance has a wide weighing range of, for example, several tons and therefore a relatively low accuracy of, for example, ±100 g. Between the metering valve and the liquid reservoir there is a buffer vessel, the weight of which can be determined by means of a precision balance and which can be sealed off with respect to the liquid reservoir in order to dispense small quantities of liquid from the metering valve. The precision balance can be used to determine the weight of the buffer vessel and the liquid which is present therein, according to the disclosure with an accuracy of, for example, ±0.1 g, and from this determination to determine the quantity of liquid which has been dispensed. The accuracy of the weight of the quantity of liquid dispensed is limited firstly by the fact that the buffer vessel is connected to the storage reservoir and the metering valve via flexible lines, which has an adverse effect on the measurement, and secondly by the fact that the liquid is not dispensed directly from the buffer vessel, but rather firstly passes via a line to the metering valve and is only dispensed by the latter. Moreover, the complex structure with storage vessel, buffer vessel and metering valve, which are connected via lines, in practice prevents the metering device from being of mobile design or being fitted to a robot arm or a linear axis system.
In view of the drawbacks of the devices of the prior art which have been described above, the invention is based on the object of providing a device which is intended to allow simplified weighing out of a desired quantity of substance.